The present invention pertains generally to injectors for delivering a medicament into a patient. More particularly, the present invention pertains to needle-free jet injectors that are useful as part of a compliance and dose monitoring program. The present invention is particularly, but not exclusively, directed to a jet injector having an integral system capable of producing and recording injection information for subsequent use in determining compliance with a prescribed dosing regimen.
Evaluating the effectiveness of drug therapies often requires information regarding dose administration. Some therapies require that the patient comply with a dosing regimen involving frequent injections administered at home or at other sites not observable by a clinician. If the dosing regimens are not followed due to a noncompliant patient, then the effectiveness of the therapy can be significantly diminished and the patient""s condition may fail to improve. Money expended on ineffective treatments is wasteful, which is a growing concern with rising health care costs.
An example of a therapy in which compliance is an issue is treating growth hormone deficiency in children. Growth hormone is a very expensive therapy costing over $10,000 per year. If the date and time that the injection is administered can be monitored, then the clinician can provide feedback to the patient or guardian to improve compliance or recommend discontinuing the therapy. Additionally, the insurance carrier may refuse to reimburse patients for therapies that are ineffective due to non-compliance.
In treating some diseases, knowledge of the actual dosing can be important for evaluating whether a particular prescribed regimen is an effective treatment for an individual patient. For example, a physician evaluating a diabetic patient""s status benefits from knowing the amount and timing of insulin injections. In this case, correlating the insulin injections with other data, such as glucose measurements, allows the physician to provide the patient with feedback for optimizing their blood glucose control, which is known to have great benefit.
Logging injector data for compliance and dose monitoring can be useful in several clinical applications. As described above, logging injector data can be useful for therapies requiring a fixed drug dosage, such as the treatment of growth hormone deficiency. Additionally, logging injector data is useful for therapies where the dosage is adjusted based on variable patient demand for the drug, such as insulin injections to control blood glucose.
For an effective compliance monitoring system, the validity of an injection together with the date and time that the injector is fired is preferably recorded. Specifically, it is useful to discriminate events that do not represent a valid injection, such as firing the injector: 1) to practice, 2) by mistake, 3) while checking device operation, or 4) as an attempt to fake an injection. In addition, the ability to capture the dose amount administered during a particular injection can be extremely useful in a compliance and dose monitoring program.
The benefits of data logging are not necessarily limited to needle-free systems, intended for self-injection or care sites not observed by clinicians. Data logging and communications could also be beneficial in a hospital or a clinic for entry of the injection into the patient""s medical record, for capturing costs, or for inventory control.
In light of the above, it is an object of the present invention to provide a data logging system for a needle-free jet injector capable of producing and recording injection information for subsequent use in determining compliance with a prescribed dosing regimen. It is yet another object of the present invention to provide a data logging system for a needle-free jet injector that can record and store the date, time and dose amount of an injection and can store data from multiple injections. Another object of the present invention is to provide a data logging system for a needle-free jet injector that can distinguish between valid and invalid injections. Still another object of the present invention is to provide a jet injector that prevents invalid injections by preventing a user from firing the injector unless the injector is positioned against the skin. It is another object of the present invention to provide a data logging system for a needle-free jet injector that is integrated with a vacuum control system for the injector. Another object of the present invention is to provide a relatively small and lightweight data logging system that is integral with a needle-free jet injector. It is another object of the present invention to provide a data logging system for a needle-free jet injector that includes a communications link to allow the system to communicate to a standard personal computer and to allow the memory of the system to be accessed and cleared by the personal computer. Still another object of the present invention is to provide a data logging system for a needle-free jet injector that draws a minimal amount of power from the battery during periods of nonuse. Yet another object of the present invention is to provide a data logging system for a needle-free injector which is easy to use, relatively simple to implement, and comparatively cost effective.
The present invention is directed to a jet injector that includes an integral data logging system for producing, recording and communicating injection information. This injection information can be subsequently used to determine compliance with a prescribed dosing regimen. For the present invention, the data logging system includes at least one electrical switch that changes state (e.g. from OFF to ON) during an injection procedure. Examples of injector switches that can be used to produce injection information include; a switch configured to change state when an injector safety is released, a switch configured to change state when the injector""s vacuum pump is activated, a switch configured to change state when the injector is triggered, a switch configured to change state when the injector""s drive bar reaches a pre-selected location within the injector tube and one or more light sensing switches to determine the position of the syringe plunger immediately prior to an injection.
In accordance with the present invention, the switch(es) are connected to an electrical circuit having an electronic memory. When a switch changes state, this information along with the applicable date and time is recorded in the electronic memory. In greater detail, the electrical circuit preferably includes an electrical power source, a microprocessor, a clock, electronic memory and a communications link. Functionally, these electronic components cooperate to record and store injection information that can be subsequently accessed via the communications link and used to determine compliance with a prescribed dosing regimen. More specifically, it is envisioned that a patient will use the injector a plurality of times over a predetermined time interval (e.g. daily for one month). At the end of the interval the patient will provide the injector to a health-care worker who will then upload the data recorded and stored in the electronic memory of the injector via the communications link. For example, the data can be uploaded to a PC at a health-care facility where the data can then be manipulated and analyzed to determine compliance with a prescribed dosing regimen.
In accordance with the present invention, the data logging system can be used to distinguish between valid and invalid injections based on the duration of medicament release from the injector. For example, if a user fires the injector into the air (i.e. an invalid injection) the duration of medicament release will be relatively small as compared to an injection into the skin where the skin provides a back-pressure that slows medicament release. To distinguish between valid and invalid injections, a first switch (hereinafter the trigger release switch) is configured to change state when the firing cap is depressed indicating the start of an injection. Additionally, a second switch (hereinafter the end-of-stroke switch) is configured to change state after the drive bar of the injector transits through the injector tube and comes to rest indicating the end of an injection. In one embodiment, a conductive drive bar contacts a conductive inner barrel after transit through the injector tube to close the end-of-stroke switch.
Also in accordance with the present invention, the electric circuit can be configured to control a vacuum system for the injector in addition to its data logging functions. Specifically, the electric circuit can include a circuit portion that connects an injector vacuum pump to the power source when the user depresses a vacuum activation switch on the injector. In a particular embodiment of the present invention, the vacuum activation switch also functions to release a mechanical safety and arm the trigger of the injector. The electric circuit in this embodiment is further configured to deactivate the vacuum pump when the end-of-stroke switch described above closes.
In another embodiment of the present invention, the injector can be configured to prevent invalid injections (while recording valid injections). In this embodiment, a pre-determined vacuum level downstream of the vacuum pump (indicating that the injector is positioned against a surface such as the skin) is required to arm the trigger of the injector. In one implementation, a safety which prevents movement of the trigger is pneumatically released when the pre-determined vacuum level is achieved. In this embodiment, the user is unable to fire the injector into the air, and thus, only valid injections can occur and are recorded.
In another embodiment of the present invention, one or more light sensing switches are disposed inside the injector tube to determine the position of the syringe plunger immediately prior to an injection. With the initial plunger position, the dose amount for the respective injection can be calculated by the data logging system and used to determine compliance.